Aloe derived scale inhibitor

ABSTRACT

A method is provided for inhibiting scale in a liquid hydrocarbon system, including the steps of: providing a liquid hydrocarbon system; providing an aloe-derived scale inhibitor; and mixing the aloe-derived scale inhibitor with the liquid hydrocarbon system in amounts effective to inhibit formation of scale. The scale inhibitor is aloe gel dissolved in water at a concentration of between about 5 and about 50% wt/wt, which includes polysaccharides having a hydrocarbon chain structure having carboxyl and alcohol functional groups that interact with divalent ions.

BACKGROUND OF THE INVENTION

Scale is a condition which affects various aspects of the crude oilproduction, transportation, and refining industry. One particular areawhich is affected is secondary reservoirs constituted mainly ofinorganic chemical compounds, presented in a system which is at leasthalf man-made. Native fluids of a formation and/or changes in thethermodynamic, kinetic and hydrodynamic conditions under which thosefluids exist and are produced can cause scale compounds to form.

Scale can reduce formation porosity and permeability when developed onthe pores of the formation, especially when this occurs near the well.Scale can also block regular flow when perforations are obstructed orwhen a thick layer forms on production pipe walls. Scale can also coverand damage completion equipment such as security valves and gasartificial lift system mandrels.

Scale formation begins when any natural fluid condition is disturbed ina way that exceeds the solubility limit of one or more of itscomponents. The first development is generally either a sodden fluidwhich is made through formation of unstable atom groups (homogeneousnucleation) or a fluid-flow limiting surface which can causeheterogeneous nucleation.

CaCO₃ is one of the more common types of scale. Its precipitationdepends on CO₂ concentration in the system, brine composition, andtemperature and pressure control over the chemical equilibrium betweenCO₂ and reservoir formation waters, according to the following reaction:

Ca(HCO₃)₂⇄H₂O+CO₂+CaCO₃

In fields where water presence is considerable or in those where waterinjection is used for secondary oil recovery, scale problems can besevere and can increase with time. If this scale is addressedmechanically, the removing methods must be carried out at increasingfrequency. Thus, it is generally desirable to prevent scale formation.This can be done as a complementary treatment after mechanical removalof scale.

Existing scale inhibitors have very specific performances, and there isno universal inhibitor for all scale types. Previously, inhibitorefficiency was evaluated by trial and error. Currently, a betterunderstanding of the thermodynamic kinetic mechanism of compound crystalgrowth allows a better evaluation of the scale inhibitor effectiveness.

In use, inhibitors are injected to the location to be treated eithercontinuously or intermittently. According to the phase where they can beinjected, inhibitors are classified as either soluble in organic phase,or soluble in aqueous phase.

The phase in which they are injected is very important since it canaffect the inhibitor efficiency. In systems with high water cuts, it ispreferred to use an inhibitor which is water soluble, because this phaseis the cause of scale incrustation and is the phase with greater contactwith internal pipe surfaces. This phase is therefore the better phasefor transporting the inhibitor to the metallic surfaces.

Most inhibitors developed to avoid scale are soluble in the aqueousphase because this phase is the main cause of deposit formation. Severalresearchers have dedicated efforts to understand crystal growthmechanisms that form scale to develop a better inhibitor based onunderstanding the inhibitor-crystal interaction.

Two ways by which the scale inhibitor operates are known. The firstmechanism is the adsorption effect, wherein the inhibitor moleculesoccupy the nucleation sites which are preferred by the crystals. Thus,crystals cannot find active places to adhere to the surface and,therefore, crystal nucleation is not promoted.

Another inhibitor mechanism is based on an adsorption model, that is, amorphologic change that can prevent formation of crystals in thepresence of the inhibitor. Depending on the inhibitor characteristicsand the nature of the substrate, it is possible that the inhibitor willbe adsorbed over the crystalline net, forming complex surfaces or netswhich have difficulty remaining and growing in active places.

Scale inhibitors are generally classified as organic and inorganic. Theinorganic types include condensed phosphate, such as polymetaphosphatesor dimetallic phosphates.

Inorganic phosphates operate on scale formation through the thresholdeffect. Through this mechanism, it is not necessary to complex all ionsin solution because, when carbonates and calcium sulfur crystals beginto be shaped, they precipitate and, at that moment, phosphate ions coverthe small nucleating crystals and crystal growth is atrophied. Coatingis given because of phosphate ion adsorption in the crystal surface.

One problem with use of polyphosphates is that in a solution,polyphosphates can suffer hydrolysis or reversion to hydrotreatedorthophosphates. Hydrotreated orthophosphates react with calcium to forminsoluble calcium phosphates. Temperature, pH, concentration, solutionqualities, different types of phosphates and the presence of someenzymes all influence the reversion velocity of these inhibitors.

There are four organic compound groups (polyphosphates,polyphosphonates, polycarboxylic and polymeliates) which have a provenchelant effect over the ions which normally form scale, and thesecompound groups are used in manufacturing scale inhibitors. Couples ofthese groups typically are used as follows: (i) phosphonate compoundswith alkaline base such as polyphosphates and polyphosphonates, and (ii)weak acids such as polycarboxilyc acid and polymeliates.

The organic phosphate compounds are limited by temperature because theycan also revert when exposed to high temperatures. Further, phosphonatesare not effective in waters having a high content of calcium ions, andshould be applied in large doses.

Polymers obtained from carboxylic acids (that is, polyacrylates) areequally used as scale inhibitors. These compounds tend to distort thecrystalline structure of the minerals formed, preventing their adhesionto other crystal and/or to metal surfaces. Temperature of use of thesecompounds is more stable than the phosphates and phosphonates, however,some polymers have limited tolerance to calcium, generally a maximumconcentration of about 2,000 ppm, although some are effective atconcentration as high as 5,000 ppm.

For an effective inhibition using these compounds, it is required toinject high polymer concentrations. Taking into account theeffectiveness of these compounds at high temperatures (where otherproducts cannot work), this treatment has been considered economical insome instances.

Recently, chelant agents are applied, for exampleethylenediaminetetra-acetic acid (EDTA), or its sodium salt, have beenused in softening water and/or as scale inhibitor. EDTA forms a solubleand stable complex with magnesium, calcium, strontium, barium and otherdivalent metals, and this prevents scale formation. This kind ofinhibitor does not suffer reversion and is stable at high temperatures.However, these inhibitors are also much more expensive than otherproducts.

Thus, conventional scale inhibitors can be summarized as follows:

Inhibitor Type Limitations Inorganic Suffer hydrolysis and canprecipitate polyphosphates as calcium phosphates because of temperature,pH, solution quality, concentration, phosphate type and the presence ofsome enzymes. Organic Suffer hydrolysis with temperature. polyphosphatesNot effective at high calcium concentrations. Must be applied in highdoses. Polymers based on Limited calcium tolerance (2,000 ppm)carboxylic acids although some can work at concentrations higher than5,000 ppm Larger concentrations are needed. Ethylenediaminetetra- Veryexpensive. acetic acid (EDTA)

According to what is known about commercial scale inhibitors, the needarises to develop products which reduce the existing limitations andwhich are flexible in application.

It is the primary object of the present invention to provide a solutionto this need.

Other objects and advantages of the present invention will appearherein.

SUMMARY OF THE INVENTION

According to the invention, the foregoing objects and advantages havebeen attained.

According to the invention, a method is provided for inhibiting theformation of scale, which method comprises the steps of providing aliquid hydrocarbon system; providing an aloe-derived scale inhibitor;and mixing the aloe-derived scale inhibitor with the liquid hydrocarbonsystem in amounts effective to inhibit formation of scale.

Still further, according to the invention, a scale inhibitor compositionis provided which comprises aloe gel dissolved in water at aconcentration of between about 5 and about 50% wt/wt. The aloe gelcomprises polysaccharides, solubilized in water between about 60° C. andabout 90° C., and has a hydrocarbon chain structure having carboxyl andalcohol functional groups that interact with divalent ions such as Ca⁺⁺,Mg⁺⁺, and the like.

Unlike chemically synthesized inhibitors that are based on theprinciples indicated above, the scale inhibitor according to theinvention is advantageously based on active ingredients identified inAloe plant gel, especially Aloe Vera. Such a scale inhibitor can beapplied at low and high calcium concentrations and without thelimitation that the composition will precipitate because of hydrolysis.In fact, with the composition according to the invention, hydrolysisfavors interaction with ions in the solution and, thus, efficiency as ascale inhibitor increases.

The scale inhibitor according to the invention is also thermally stableup to a temperature of at least approximately 125° C. The inhibitor cantherefore be applied in production management surface installations, andin other manufacturing equipment operating at lower temperatures, and inrelatively shallow oil wells where such temperatures are not reached.

The present invention advantageously provides a solution to scaleproblems, and the solution is based upon a composition which isformulated from a plant, and which can be practiced at a decrease incosts because it is not a chemically synthesized compound. Thecomposition of the present invention also reduces environmental impactsince it is biodegradable and fosters other local economy sectors suchas agriculture.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of preferred embodiments of the present inventionfollows, with reference to the attached drawings, wherein:

FIG. 1 illustrates an Aloe Vera plant and parts of the plant which arestarting raw materials for the present invention;

FIG. 2 schematically illustrates an egg-box model showing one mechanismby which the composition of the present invention operates;

FIG. 3 schematically illustrates the steps of formation of thecomposition of Example 1;

FIG. 4 schematically illustrates the steps of formation of thecomposition of Example 2; and

FIG. 5 schematically illustrates various industrial and domesticprocesses with which the composition and method of the present inventioncan be utilized.

DETAILED DESCRIPTION

The invention relates to a composition and method for inhibiting scalein various industrial and domestic systems, one example of which is awater driven secondary oil production well. Various influences can causescale formation on surfaces of the facility, and this scale caninterfere significantly with proper operation of the facility. Accordingto the invention, a composition is provided which is useful forinhibiting scale formation, and this composition overcomes the variousdrawbacks of known compositions as outlined above.

According to the invention, the scale inhibitor composition isadvantageously derived from aloe plants, preferably from Aloe Vera, andthe composition derived in this manner is not adversely affected byhydrolysis, is suitable for use at temperatures up to at least about125° C., and is affordably obtained from agricultural sources.

Aloe Vera is a xerophile plant originated in tropical or subtropicalzones. This plant is characterized by firm and erect lance-shaped leaveswith toothed sides and a sharp point. Referring to FIG. 1, the leafepidermis has a thick cuticle or rind 10. Under the epidermis is themesophyll which is differentiated by clorenchimas cells and a thincellular wall, known as parenchyma 20. The cellular parenchyma surroundsa jellied, transparent and mucilaginous material, referred to herein asa gel 30. Moreover, vascular packages of the plant have interior cellpackages which contain a yellow sap, or aloes, which are found betweenthe two major cells.

According to the invention, the gel of Aloe Vera which is used toprovide a scale inhibitor. This gel contains various chemical compoundsincluding amino acids, glucosides, minerals and vitamins. The specificcomposition of a particular specimen is not constant because thiscomposition varies according to soil variations, season of the year,plant age and climate. However, the aloe gel does at all timesconstitute hydrocarbon chain structure having carboxyl and alcoholfunctional groups. The functional groups interact with, or complex with,divalent ions which cause scale such as Ca++, Mg++ and the like.

The gel represents the succulent part of the leaf once the skin iseliminated. Aloe and other xerophile plants stock water when hightemperatures evaporate humidity from the soil. Thus, when ambientgrowing temperatures increase, the quantity of gel in the leavesincreases as well.

Aloe-derived gel according to the invention can be used to produce ascale inhibitor having reactivity with calcium to form gels whichencapsulate the calcium. This is believed to occur according to anegg-box model (FIG. 2), which assumes that calcium ions serve as abridge to form ionic liaisons between two carboxyl groups belonging totwo different chains in close contact. According to this polysaccharidemodel, the chains interact with Ca⁺⁺ allowing a structure coordinatedpackaging. FIG. 2 shows how chains of the gel interact with Ca⁺⁺ to gettogether. This causes stability when systemic forces or other conditionswould otherwise try to revert the gel to an original condition.

The interaction strength between calcium and other oxygen atoms in thepolysaccharides implies coordination liaisons used by the calcium emptyorbital. Oxygen atoms of the hydroxyl groups, the ring oxygen atom, andthe oxygen atoms of sugars combined by hydrogen bridges participate inthe liaison process through free electrons. Calcium is favored tocomplex with polysaccharides because the ionic radius of calcium (0.1nm) is large enough to coordinate with the spaced oxygen atoms of thegel, and also due to the flexibility presented by the coordinatedliaison addresses.

Biopolymers, hydrophilic molecules in a soluble matrix, and othercompositions existing in aqueous solutions tend to control CaCO₃ crystalformation.

The acid group presence from gels of the present invention, for examplesuch as carboxylic acid (—COOH) in soluble protein molecules, interactswith calcium ions (Ca⁺²), controlling crystallization. Position anddistance of the acid groups in the macromolecules can cooperate to putcalcium ions together.

On the other hand, biopolymer adsorption in specific faces of the CaCO₃is a key element to control the crystallization process.

Biomacromolecules can induce CaCO₃ crystal polyforms. Crystallizationwith biopolymers induces phase transition of the calcite crystal intoaragonite.

According to the invention, a formulation is provided for themanufacture and application of products based on Aloe plants, especiallyAloe Vera, as a scale inhibitor.

The composition of the present invention demonstrates efficiency up to80% at trial conditions established by the standard NACE TM 0374, whileefficiency of commercial inhibitors is only between about 15% and 38% atthe same trial conditions.

The composition of the present invention possesses inhibition mechanismsdirected to calcium carbonate crystal nucleation changes. Thecomposition also can be used at high and low calcium concentrations. Thecomposition of the present invention does not precipitate because ofhydrolysis, and is thermally stable up to 125° C. Use of the compositionof the present invention provides a cost reduction because thecomposition is not chemically synthesized. Finally, the composition andmethod for making and using same is environmentally friendly technology,and encourages national economy through the encouragement ofagro-industry.

The composition of the present invention can be made from a raw materialin the form of dehydrated Aloe Vera gel, preferably having thecharacteristics as set forth in Table 1:

TABLE 1 Aloe Vera gel characterization. Property Average Chemicalstructure Hydrocarbon chain structure with carboxyl (COOH) and alcohol(OH) functional groups Elemental composition C 29.0-32.0; H 4.2-6.5; O44.0-55.0; N 0.4-0.8; S 0.3-1.6; Ca 2.3-5.2; Mg 0.8-1.0; P 0.3-0.4.Average molecular 25 KDa (kilo-Dalton) weight, determined byviscosimetry Thermal stability Up to 125° C.

While in solution, Aloe Vera gel has properties as set forth in Table 2below:

TABLE 2 Aloe Vera gel aqueous solution characterization. PropertyAverage pH 3.8 Calcium 3.75% wt/wt Magnesium 0.9% wt/wt Acidity (TAN)18.33 meqKOH/g Intrinsic viscosity 0.4 dL/g Fluid type NewtonianCritical Concentration 15% wt/wt

The composition set forth above is representative of the raw material(Table 1) used in preparation of the composition of the presentinvention, and a preferred embodiment of the resulting gel solution(Table 2). Of course, other starting raw materials can be used wellwithin the broad scope of the present invention.

The scale inhibitor composition of the present invention is a solutionof aloe gel in water, preferably at a concentration of between about 5and 50% wt/wt, more preferably between about 10 and about 25% wt/wt,most preferably 15% wt/wt.

Two methods were used to formulate scale inhibitors according to thepresent invention. The resulting products are referred to herein asBio-Inh1 and Bio-Inh2. As demonstrated below, each of these products haswell defined scale inhibitor characteristics.

Example 1 Preparation of Bio-Inh1

A crop of Aloe Vera plants was developed, and isolation and purificationof the Aloe Vera gel was conducted using known techniques such as thosedisclosed in US2003/0211182A1. The Aloe Vera gel is processed tosterilize and stabilize same. The sterilized and stabilized Aloe Veragel is then dissolved in H₂O, stirring continuously at a temperature ofbetween about 60 and about 90° C. to prevent enzymatic reactions and/orbacteria agent actions that cause organic material degradation.

A solution of the gel in water was formulated having a concentration ofbetween about 5 and about 50% wt/wt. An abrupt change in solutionconductivity and viscosity is observed, especially at a concentration ofabout 15% wt/wt. This concentration is therefore desirable and isapplied to a system to inhibit scale. FIG. 3 schematically illustratesthis formulation process.

Example 2 Preparation of Bio-Inh2

A crop of plants was developed, and isolation and purification of theAloe Vera gel was conducted using known techniques. The Aloe Vera gel issterilized and stabilized. A 20 gram sample of Aloe Vera gel was mixedwith 100 ml of methanol. This mixture was continuously stirred for 10minutes, and then decanted for 30 minutes. The resulting product wasfiltrated, and the insoluble fraction was collected. This fraction isreferred to herein as the MPS (Solid Precipitable Methanol,polysaccharides plus a salt complex insoluble in alcohol, and organicacids). The MPS was dried in a heater at 30-50° C. for 2 hours toproduce sterilized and stabilized MPS. The sterilized and stabilized MPSis then dissolved in H₂O, stirring continuously at a temperature ofbetween about 60 and about 90° C. to prevent enzymatic reactions and/orbacteria agent actions that cause organic material degradation.

A solution was formulated having a concentration of between about 5 andabout 50% wt/wt. An abrupt change in solution conductivity and viscosityis observed, especially at a concentration of about 15% wt/wt. Thisconcentration is therefore desirable and is applied to a system toinhibit scale. FIG. 4 schematically illustrates this formulationprocess.

The Bio-Inh1 and Bio-Inh2 products were formulated to solve scaleproblems presented in the oil and gas value chain, and exhibit excellentproperties in this use. It should also be noted, however, that they canalso be used in processes involving water management that involveinorganic compound precipitation processes due to hardness, such as heatexchange equipment, and many others. In this regard, FIG. 5schematically illustrates a wide variety of oil and gas value chainprocess stages where the composition of the present invention canadvantageously be utilized. Examples of such process stages include,hydrocarbon producing wells, collection and compression systems,injector wells, water and oil separation plants, sweetening plants,dehydration plants, industrial consumption sites, domestic consumptionsites, LGN plants and transportation facilities.

It should be appreciated that the present invention provides a processof formulation, manufacture and application of a scale inhibitor basedon the active principles identified in aloe-derived plant gel,especially Aloe Vera. The present invention has advantages over existingcommercial products because it can be applied at low and high calciumconcentrations and does not precipitate due to hydrolysis. In fact, withcompounds of the present invention, hydrolysis favors interaction of thecomposition with ions in the solution, thereby increasing the efficiencyas a scale inhibitor. Further, compositions according to the inventionare thermally stable to temperatures of at least about 125° C. Thus, thecomposition can be applied on production management surfaceinstallations, industrial equipment operating at acceptable temperaturesand in shallow to moderately deep wells where such temperatures are notreached.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible of modification of form, size, arrangement of parts anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within its spirit and scope as defined bythe claims.

1-11. (canceled)
 12. An aloe-derived scale inhibitor, comprising aloegel dissolved in water at a concentration of between about 5 and about50% wt/wt, wherein the aloe gel comprises polysaccharides having ahydrocarbon chain structure having carboxyl and alcohol functionalgroups that interact with divalent ions.
 13. The aloe-derived scaleinhibitor of claim 12, wherein the aloe-derived scale inhibitor isthermally stable up to a temperature of at least about 125° C.
 14. Thealoe-derived scale inhibitor of claim 12, wherein the aloe-derived scaleinhibitor has an average molecular weight of between about 15 and about50 KDa.
 15. The aloe-derived scale inhibitor of claim 12, wherein thealoe derived scale inhibitor is soluble in water.
 16. The aloe-derivedscale inhibitor of claim 12, wherein the aloe gel comprisespolysaccharides which complex with divalent ions.